This invention relates to metered dose dispensing aerosol valves and in particular to metered dose dispensing valves suitable for use with metered dose inhalers.
Conventional metering valves for use with pressurised dispensing containers comprise a valve stem co-axially slidable within a valve member defining an annular metering chamber and outer (diaphragm) and inner (tank) annular seals co-operative between the respective outer and inner ends of the valve stem and the valve member to seal the metering chamber therebetween. The valve stem is movable between a non-dispensing position in which the metering chamber is connected to the container and charged with product therefrom. The valve stem is movable, generally against the action of a spring, to a dispensing position where the metering chamber is isolated from the container and vented to the atmosphere for discharge of the product.
Loss of prime and loss of dose are dosing anomalies that are commonly encountered with metered dose inhalers. Loss of prime occurs when vapour or air gets trapped in the metering chamber. Unless primed immediately before actuation, the time since the previous actuation can be major variable as can the conditions under which the product has been stored; such as unit orientation and temperature. The after phenomenon is partly as a result of drug substance in the metering chamber being lost from the chamber prior to actuation of the valve. Drug substance may be lost from the metering chamber due to the ability of the active substance to migrate into and out of the metering chamber during the storage period.
EP-A-0692434 discloses an aerosol valve having flow passages connecting the metering chamber to the container when the valve stem is in its rest position and having an annular gap which is dimensioned to allow flow from the container into the metering chamber but is sufficiently small so that capillary forces prevent liquid from flowing through the gap under only gravitational force. However, this arrangement would not prevent passage of sedimented material out of the metering chamber into the region of the valve between the metering chamber and the annular gap. Also, it is difficult to mass produce valves to the tolerances required to ensure effective operation of such a valve. In other embodiments of EP-A-0692434 the valves are designed so that the metering chamber is completely sealed when the valve stem is in its rest position and the metering chamber is only filled when the valve stem is intermediate between its rest and firing positions.
GB-A-2206860 and GB-A-2345279 disclose valves having a mechanical one-way valve positioned in an enclosed pre-metering region which allows the metering chamber to be filled in the rest position of the valve stem but prevents material leaving the pre-metering region of the valve to the container. However, the arrangement does not prevent passage of sedimented material from the metering chamber to the pre-metering region of the valve.
It is desirable to provide a metered dose dispensing aerosol valve in which the problems of loss of prime as well as loss of dose are substantially reduced.
According to the present invention there is provided a metered dose dispensing aerosol valve for a container comprising a valve body defining an aperture, a seal mounted at the aperture, a metering chamber, a tank seal, a transfer passage through which a quantity of substance to be dispensed can pass from the container into the metering chamber and a valve stem having a dispensing passage, the valve stem being slideably moveable through the seal such that in a first position the dispensing passage is isolated from the metering chamber and the metering chamber is in communication with the container via the transfer passage and in a second position the dispensing passage is in communication with the metering chamber to allow substance to be dispensed from the metering chamber through the dispensing passage and the transfer passage is isolated from the metering chamber, and the valve stem extending, at least in the second position, through the tank seal, wherein the transfer passage comprises a mechanical flow valve positioned towards the end of the transfer passage adjacent the metering chamber, which in said first position, allows substance to be dispensed to pass from the container into the metering chamber but not out of the metering chamber.
The invention provides a one-way flow valve which freely allows substance to enter the metering chamber from the container when the valve stem is in its first (rest) position but provides a barrier to prevent substance leaving the metering chamber. Thus, after actuation and the valve stem is returned to its rest position, the metering chamber is immediately charged from the container and thereafter migration of substance from the metering chamber is prevented. More particularly, the mechanical flow valve is normally biased into a closed, sealed state and is displaceable when the valve stem is in its first position to allow substance to be dispensed to pass from the container into the metering chamber, and once the metering chamber is filled, the flow valve returns to its sealed state. Thus, loss of prime and loss of dose is substantially reduced or eliminated.
In one embodiment of the invention the transfer passage is formed within the valve stem and has an outlet from the valve stem which is positioned within the metering chamber when the valve is in the first position. The flow valve conveniently comprises a displaceable seal positioned at said outlet which may be in the form of an elastomeric sleeve or ring extending around the valve stem.
In a second embodiment the transfer passage is formed within the valve stem and has an outlet from the valve stem which is positioned within the metering chamber when the valve is in the first position. The valve stem extends in the first position through the metering chamber in sealing engagement with the tank seal and the tank seal is configured to provide a displaceable elastomeric seal over said outlet from the valve stem of the transfer passage.
In a further embodiment, the valve stem is in sealing engagement with the tank seal, at least in its second position, and the transfer passage is defined between the tank seal and the valve stem when the valve is in its first position. The transfer passage may be annular, being formed completely around the valve stem or the valve stem may have a cut away portion to form the transfer passage. In either case the valve stem may have an elastomeric stem seal secured thereto, which may seal against the tank seal but is displaceable to allow passage of substance from the container through the transfer passage into the metering chamber.
In a further embodiment the inner end of the valve stem has a seal support plug secured thereto, the seal support plug extending through a tank seal in sealing engagement therewith when the valve stem is in said first position, the sealing support plug having one or more apertures forming said transfer passage which are covered by a displaceably annular elastomeric seal located between the top surface of the seal support plug and the inner end of the valve stem.